The present invention relates to a new and improved drive control for a transportation system, especially an elevator containing a drive or displacement motor coupled to an eddy current brake and to a tachometer. The drive control comprises a reference or set value transmitter and a regulator which is connected at its input side to the tachometer and at its output side to an adjustment or control member for controlling the driving torque of the drive motor as well as to an adjustment or control member for controlling the braking torque of the eddy current brake. The reference value transmitter generates an increasing reference or set value for the acceleration and a decreasing reference or set value for the deceleration. The travel course of the elevator is regulatable as a function of a regulation deviation which is supplied to the regulator and which is formed from the difference of the reference or set value and the actual value generated by the tachometer.
In a similarly conceived drive control as known, for example, from U.S. Pat. No. 2,828,832, granted Apr. 1, 1958, and the Canadian Pat. No. 579,898, the travel course is regulated only during the deceleration phase for the purpose of a precise direct approach while the other phases of travel of the elevator proceed without regulation. Upon initiating the deceleration phase the drive motor is turned off and the reference value transmitter is activated. The reference value voltage generated as a function of distance or travel by the reference value transmitter is connected in opposition to the actual voltage value generated by the tachometer generator. The voltage difference resulting therefrom is fed to the input of a regulator composed of an amplifier. At its output side the regulator is connected with an adjustment or control member constituted by a thyratron rectifier which controls the excitation current of the eddy current brake when a negative regulation deviation occurs. To improve the travel curve during the acceleration phase the asynchronous motors used in such drive controls as drive motors are equipped with a starter winding or coil. Thus, the drive motor as described, for example, in Swiss Pat. No. 437,698 may be designed as a pole-switchable drive motor having six or four poles and the start may be affected using the higher number of poles while a change to the smaller number of poles is affected when a predetermined velocity is reached.
In the drive control as described hereinbefore, the travel course is uncontrolled with the exception of the deceleration phase. No optimum results are achieved, therefore, with reference to the travel comfort which depends upon the jerk and acceleration values as well as with respect to travel time. A further disadvantage of this control is that the braking or stopping distances have to be smaller than the smallest storey distance which will result in too small rated travel speeds in consideration of the values for the deceleration which are still permitted.
In a drive control as initially described and as known, for example, from U.S. Pat. No. 2,958,796, granted Nov. 1, 1960 the asynchronous motor used as the drive motor is coupled to the elevator hoisting winch by an eddy current clutch as well as to the eddy current brake and to the tachometer generator. The excitation winding of the eddy current clutch is arranged in the operating circuit of a thyratron rectifier serving as an adjustment or control member for controlling the drive torque. The excitation winding of the eddy current brake is positioned in the operating circuit of a further thyratron rectifier serving as an adjustment or control member for controlling the braking torque. The control current circuit of the thyratron rectifiers are connected to the outputs of a regulator such that the excitation currents of the clutch and of the brake are controlled in opposition to each other. The regulator comprises an amplifier including a pentode and operates in such a manner that during the acceleration phase the drive torque is progressively controlled as a function of the positive regulation deviation and during the deceleration phase the brake torque is progressively controlled as a function of the negative regulation deviation. The reference value voltages generated by the reference value transmitter are tapped off at a capacitor, and the reference value for the acceleration is formed during charging of the capacitor and the reference value for the deceleration is formed during discharging of the capacitor.
The drive control as described hereinbefore contains certain disadvantages. Thus, the equipment costs, for example, are significantly increased and more space is required by virtue of the provision of the eddy current clutch. Also, the regulation by means of a time-dependent reference or set value during the deceleration phase no longer satisfies the requirements in respect of a precise direct stopping in modern day elevator systems. It is a further disadvantage that the driving torque as well as the braking torque are effective during the acceleration phase and the deceleration phase, whereby additional energy is consumed.
In another prior art drive control as known, for example, from German Pat. No. 2,340,930 the last-mentioned disadvantages are partially avoided. For controlling the driving torque, and as is known, the winding or coil of the drive motor directly coupled to the eddy current brake and to the tachometer generator is powered by an adjustment or control member composed of thyristors which are controllable by means of a firing angle control. The reference value generator generates a time-dependent increasing reference value voltage for the acceleration phase and a distance-dependent decreasing reference value voltage for the deceleration phase. The regulating circuit for the rotational speed of the drive motor comprises one respective regulator for at least two phases. The regulating circuit for the rotational speed of the eddy current brake comprises a further regulator, the output of which is directly connected to a control or adjustment member of the eddy current brake which comprises a controllable thyristor rectifier. The reference or set value voltage and the actual value voltage generated by the tachometer generator are supplied to the input side of all three regulators.
It is a disadvantage of the last-mentioned drive control that in an inertia-prone regulation path, as constituted by an eddy current brake, relatively large delays occur, whereby the stability of the regulating circuit decreases. Further disadvantages are that at least three regulators are required for regulating the rotational speed of the drive motor and the eddy current brake and that the provided reference value transmitter transmits a time-dependent reference or set value during the acceleration phase, so that no optimum total travel curve can be achieved.